Valve motion measurement is commonly performed during engine tests, but serial equipment for continuous valve lift monitoring can be required for those applications with variable valve opening systems. Typically, a sensor (generally a proximity or laser sensor) is pointed to the valve head to measure the movement of the valve. However, in order to install these sensors, holes should be machined within the cylinder head, to position the sensor supporting elements. This is a long, complex and costly process. Furthermore, on typical valve motion measurements for development purpose, the sensor points towards the upper part of the valve head, which is filleted. Since the sensors require a flat target surface, a properly machined valve should be used during tests.
The valve head is subsequently weakened and this prevents tests to be run with combustion, meaning that only measurements on test rigs are commonly allowed. In addition, the preparation of the cylinder head and valves for the test can take a relatively long time, and the modified valves may not behave exactly as serial (standard) components. Due to the modifications required by the standard approach, all the components used for testing (cylinder head, valve assembly, valve actuation) have to be considered as disposable with subsequent hardware costs.
Still within the standard way to test valve motion, the sensor can be pointed towards the combustion face of the valve. The valve shall not be modified, but the positioning of the sensor requires the cylinder block to be removed and this obviously prevents all tests with combustion. Actually this is a general limit for these kind of tests, because modifications in the engine hardware may in fact cause oil or fuel leakages. Operations on the sensor (e.g. the setting of the “zero” position of the valve) after the sensor is in place are also usually uncomfortable, because of tight room available, especially if the engine is already assembled. Moreover, the sensor can be damaged during combustion due to too high temperatures.
With such an approach, tests without combustion cannot provide a detailed picture of the valve train performance of the real engine, and specifically of the valve opening and closing dynamics. As an alternative, indirect measurement of the position of the valve (e.g. by strain gauges mounted on valve train components) have proven not to be enough reliable, in particular because of the difficulties in the interpretation of the output of these kinds of sensors.